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Subject: Re: Evaluation by neural network ?

Author: Steve Maughan

Date: 06:48:36 11/10/97

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I've some experience of neural networks and I don't think it would be
possible to generate a practical evaluation function with them.
Although neural networks can cope with non-linearity (eg a knight may or
may not be worth 3 points if positioned on e5), the huge range of
non-linearity involved in chess positions would defeat the non-linear
training algorithms.

Another reason for shying away from neural Networks would be the time
required to evaluate a position.  Due to the complexity of neural
networks they usually use floating point maths (but I guess that could
be substituted for lookup table) and require the calculation of
intermediate values (hidden layers).  This would greatly slow down the
search compared to a linear evaluation function and would therefore need
to give a much more accurate positional evaluation to compensate.

Also a complete evaluation will need to be carried out at the leaf nodes
since a non-linear element of evaluation may be altered by the last move
in the search chain (eg the last move Nf3 alters the value of the Bishop
on a7).  This means that a program cannot perform incremental
evaluation, slowing it down even further.

I don't want to sound too negative but I really think it would be tough
to develop a chess program based on Neural networks.  However Go or
Othello are far more likely to be suitable!

Regards

Steve Maughan



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